1. Field of Invention
The present invention relates to an improved high-capacity apparatus for rapidly pressure treating a large surface area, such as the hull of a cargo ship or a large storage tank, using high-pressure spray. The apparatus conforms to the surface to be treated and provides the treating power of multiple rotating or oscillating nozzles, or rotating brushes. Conformity is important in that optimal treatment requires spray nozzles to be spaced a predetermined distance from the surface being treated. Further, conformity allows for an improved seal around the treatment apparatus for collecting and recycling fluids, volatile emissions or abrasives used and for capturing any material removed from the surface during treatment. Multiple rotating nozzle units increase the area of coverage per pass of the apparatus, thus reducing the amount of time required to treat a large surface. The invention further relates to means for positioning the apparatus against a non-horizontal surface and moving the apparatus along the surface for continuous surface preparation.
2. Discussion of the Related Art
Cargo ships travel long distances through salt water. Over time the outer surface of the ship hull becomes covered with marine growth, which increases drag and reduces the operating efficiency of the ship. The corrosive action of salt water causes the hull to corrode, which can lead to metal fatigue and hull damage. It is thus necessary to periodically clean, prepare (e.g., etch), and repaint the hull of the ship. This requires lifting the hull from the water in a dry dock facility.
Dry dock work is both equipment and labor intensive. Hull surface cleaning and preparation prior to painting must be accomplished to a high level of quality, and must pass inspection by the ship's master. If a hull fails to pass inspection, it must be re-treated. The expense of re-treatment can cause the contractor to loose any profit he may have made on the contract.
Obviously, while the ship is in dry dock it is out of commission and not operating for profit. The longer the ship is in dry dock, the greater the economic cost to the ship owner. There is thus a need to clean and prepare a hull as quickly as possible. Equipment available today is not capable of rapidly treating large surface areas, particularly surfaces that are curved and/or non-horizontal.
Additional significant problems with hull preparation relate to concerns over pollution by material removed from the ship hull during the pressure treating. This material may be entrained in liquids or abrasives used in pressure treating the hull, or may be airborne particulate or volatile chemical matter. Environmental laws mandate strict measures for collecting this waste and then disposing of the collected waste. Many shipyards today are not capable of meeting these requirements.
Further yet, noise evolved by equipment used in high-pressure treatment can represent a risk to the health of the operator and other dock workers.
Other examples of structures that have large surface areas that need cleaning include buildings, elevated water tanks and storage tanks. Specifically, storage tanks of the type used for storing crude oil, chemicals and other large quantities of liquid or solid material. Storage tank cleaning is very much like cleaning the hull of a cargo ship. The owner of the storage tank must follow similar regulations with regard to the containment of the hazardous waste byproducts created during the cleaning process, i.e. paint, rust, sludge etc.
Presently, surface-treating jobs can take several days to several weeks. Most surface blasting machines (sand blasting, ball or shot peening, etc.) and abrasive cleaners in use today are designed to remove all coatings and rust down to bare metal. In most cases, such excessive cleaning is not necessary. The preparation of a ship hull for painting merely requires that surface materials are removed down to a good layer of paint or epoxy to which the new layer of primer or paint can bond. There is thus a need for a method for preparing a surface which is faster and which does not remove excessive amounts of material.
The pollution problem created when cleaning cargo ship hulls and storage tanks is so widespread that many governments (foreign, federal and state) regulations are requiring total containment of the structure during the cleaning process, e.g., by providing a framework around the structure and then draping canvas or shrink-wrapping plastic over the structure. This may take days or weeks to rig. Once the ship hull or storage tank is cover cleaning is done under the containment material. Even where the structure has been covered, there is no guaranteed against air-borne particulate and gaseous leakage and liquid runoff during the cleaning operation. Due to the large surface area, canvas or plastic are easily damaged or removed by the wind. Once the containment covering is blown off by the wind, it may takes several days to re-contain the ship or storage tank.
Yet another hazard associated with attempting to contain evolved hazardous materials stems from the accumulation and concentration of hazardous or flammable materials inside the containment zone. When cleaning or painting ship hulls or storage tanks using conventional apparatus, air-borne fine particulate material and evolved gasses accumulate within the containment material, usually in the upper areas. Most of these evolved materials are hazardous to- humans and/or highly flammable, and any type of igniter (e.g., arcs and sparks from electrical machinery, dropped molten metal from welding operations, etc.) coming in contact with the upper layer of the containment material can cause an explosion or fire. Further, in some cases other services must be performed by dockyard workers at the same time that the ship hull is being cleaned, that is, these personnel must work under the containment material. Personnel near the cleaning operation may wear protective garments and particulate filtration breathing gear. Workers inside the ship, in most cases, would not be wearing protective gear. Thus, as the concentration of hazardous or flammable materials increases, the risks to the safety of the personnel working inside the containment area increase. Finally, it has been found in practice that containment material does not prevent the waste materials from running off the ship and entering the ground or water around the shipyard.
Presently no apparatus is available which is capable of cleaning and preparing a large non-horizontal and non-planar surface areas in a short period of time, to the high standards required to pass the scrutiny of a marine inspection, without serious noise emissions, and without violating EPA standards. Even though violation of legally mandated containment standards can bring fines and jail time, violation continues to be the practice rather than the exception, since no equipment is presently available which can meet the environmental standards in a cost-effective manner.
Various specialized devices have been developed for surface treating metal surfaces. "Vactrax", available from TMR Associates Inc., cleans surfaces to bare metal using 40,000 PSI water pressure at 6 GPM, has a cleaning width of 8 to 8.5 inches. The device uses 4 to 10 inches of mercury vacuum to suction adhere to the side of a ship, and can recover and capture waste. Such a device is not suitable for preparing ship hulls prior to repainting for four reasons. First, due to the very narrow cleaning width, it would take a very long period of time to surface treat a large hull. Second, the device is designed to completely remove paint from steel. Most ships merely require cleaning and preparation of surfaces, and do not require complete removal of paint. Third, as much as 225 horsepower may be required to maintain the vacuum required to suction adhere the device to a vertical surface. Such a machine is costly to operate and maintain. This is a waste of power. And fourth, any interruption in vacuum or any break in the seal between the device and the surface can cause the device to break free and fall--a significant danger, considering the weight of such a device.
"Hydro-Crawler" available from Jet Edge.RTM., a Division of TC/American Monorail, Inc., uses powerful permanent magnetic tracks to secure to any steel surface such as a ship hull. It cleans a path up to 19 inches wide at 40,000 PSI, and thus completely removes any coating from steel. In addition to being slow, such a magnetic track vehicle is difficult to turn and maneuver.
"U-Robot System Polishing Robot--Type: UM" and "Abrasives Blasting Robot--Type: UA" available from Urakami Research & Development Co., Ltd. use vacuum to suction adhere and to vacuum clean, and use polishing cloths or abrasives. Depending upon model, the vacuum pump motor must be operated at 22 to 90 Kw. The unit cleans only one swath and travels at a speed of only 6 to 9 meters per minute. This system removes all paint to the bare metal, which is not necessary.
"Aquablast.RTM.-Plus" available from Hammelmann Corp. uses ultrahigh pressure water jets at flow rates of up to 33 L/min and pressures up to 2,500 bar to remove paint coatings and rust from the hull. It cleans and vacuums, and suffers from the above listed defects.
"The Robotic Climber.TM." available from Bartlett Services, Inc. of Plymouth, Mass., applies up to 36,000 PSI hydropressure to remove coatings from flat metal surfaces, and uses a powerful vacuum system to adhere to surfaces and to recover stripped waste. The device is only capable of treating surfaces at a rate of between 150 and 1,000 sq.ft. per hr.
"The Blast-Droyd" is available from Burds L. L. C. and is covered by U.S. Pat. No. 5,685,767 (Burds) teaches a sandblasting system including two principal components: a trolley which is located on the flat upper surface of the object to be sandblasted and a blasting machine with an oscillating blast nozzle that is carried by the trolley. The blast machine is suspended from hoist cables, whose ends are carried by the trolley. The blast machine includes a hoist drum for gathering or releasing the cable to raise or lower the blast machine along the vertical surface. For cleaning horizontal surfaces, the blast machine is carried by the trolley itself and oriented so as to direct the sand blast in a downward direction. The device is thus designed for cleaning only horizontal or perfectly vertical surfaces. The blast machine carries a mechanism for oscillating the blasting nozzle and the hoist drum within a housing to protect the moving parts from the harsh operating environment.
A review of patent literature shows that various other attempts have been made to address aspects of these problems. U.S. Pat. No. 5,628,271 (McGuire) teaches a method and apparatus using ultra-high pressure water jet to remove coatings, paint, deposits, and organic and inorganic materials from the hull of a ship. The apparatus uses a steered magnet vehicle supported by the adhesive force only of a permanent magnet to the surface to be treated. The apparatus cleans the surface of a ship hull at a rate of about 150 to about 400 square feet per hour with water at 60,000 psi using five to fifty gallons per minute. This rate of treatment is too slow to be considered for treating the large surface area of a hull of a cargo ship in a dry dock. Further, pumps for supplying fluids at such high pressures are expensive. There is also a risk of detachment if the tracks run over a non-ferrous or rusty area.
U.S. Pat. No. 5,489,234 (Hockett) and U.S. Pat. No. 5,309,683 (Hockett) both teach an apparatus which projects a cleaning material such as sand, water or the like from a nozzle to impact upon a surface to be treated, such as the hull of a ship. A fluid seal means provides a seal between a housing and the surface being treated. A vacuum source is connected to the housing for withdrawing the impacted cleaning material and surface material removed from the surface. The apparatus may be suitable for treating small areas of a ship hull, but is not suitable for treating a large hull in a short period of time while a ship is in dry dock. Further, the apparatus is rather complex, and the means for controlling the placement and movement of the apparatus is complex. Rams are used to adjust the distance between the nozzles of the treatment apparatus and the surface to be treated. Air cylinders extend the rams for adjusting the housing relative to the nozzle for varying the distance between the nozzles and the surface. A computer is preferably used to control the movement of the rams, which further increases cost and complexity of the system. Also, these rams have to make contact with the surface to sense and adjust distance. There are advantages to not contacting the surface to be treated.
U.S. Pat. No. 5,441,443 (Roberts) teaches an apparatus for blast cleaning surfaces at from 45 degrees upward to 45 degrees downward from vertical. This apparatus includes a housing, a blast assembly, a motor for rotatably driving the blast assembly, and a hopper. Different hoppers are required for surfaces of different angles. As the inclination of the curved surface changes, hoppers must be exchanged in order for the apparatus to work properly. There is thus a need for an apparatus that can work on any curved surfaces at any inclination, thus eliminating the need for the exchange of components.
U.S. Pat. No. 5,775,979 (Coke et al) teaches an enclosed abrasive blasting apparatus for a ship hull or other working surface, comprising a movable and adjustable boom, and an enclosed containment cabin for the operator and the abrasive tool mounted on the boom. The containment cabin has a top, sides, back and bottom, an adjustable angle open front, and a gum rubber seal for placing against the working surface. The outlet nozzle for the abrasive blasting system is positioned within the containment cabin, and the operator directs the nozzle against the working surface. A waste collection system creates a negative pressure in the containment cabin, which seals the cabin against the working surface and directs waste particles to a sealed collection container below the cabin. Such an apparatus would not be able to clean the large surface area of a cargo ship hull in a short period of time.
U.S. Pat. No. 5,540,172 (Goldbach and Salzer) teaches the use of an apparatus for performing external surface work on the underside of a ship hull. Towers are placed around a ship in dry dock, a shroud is used to create an enclosed workspace between the towers and the ship, and an air processing system ventilates air in the space. For abrasively blast cleaning the bottom of a ship hull, an upwardly facing closed cycle abrasive wheel is mounted on moderately articulable rails of a mobile carrier. The abrasive wheel has a compliant seal projecting forwards around its frontal perimeter. A control panel is provided to extend and retract rail end support jacks of the carrier frame for locally conforming the vertical positioning of rail ends to the bottom of the ship. This device can only be used for treating the bottom surface of the ship, and is not fully contained.
U.S. Pat. No. 4,545,156 (Hockett) and U.S. Pat. No. 4,139,979 (Hockett) teach a universal abrasive cleaning apparatus. A plurality of nozzles are connected to the distal end of a series of arms. Abrasive and fluid are conveyed through the arms to nozzles. A microcomputer receives rotational position information from sensor means and directs the stream of abrasive and fluid emitted from the nozzles to trace a particular geometric pattern thereby cleaning the area of the work surface. While this apparatus may be suitable for cleaning complex areas, it is not suitable for cleaning a large surface area such as an entire ship hull.
When high pressure water is jetted from a single nozzle, washing or stripping occurs only linearly as the nozzle is moved, and thus the operating efficiency is low. Operating efficiency is improved by associating the nozzle with a rotary spray arm which rotates rapidly in a rotational direction opposite from the impingement angle as a result of reactionary and ground effects of fluid escaping under pressure from the spray nozzle. As the spray device is moved over the surface, a broad cleaning pattern is described by the combination of the rotating rotary spray arm and the linearly moving apparatus. U.S. Pat. No. 5,456,412 (Agee) provides a pressure cleaning device approximately the size of a small lawnmower. The device is suitable for cleaning driveways, but is not suitable for cleaning non-horizontal surfaces, or for cleaning large surface areas in short periods of time, or for stripping paint from metal surfaces.
U.S. Pat. No. 5,078,161 (Raghavan) teaches an apparatus to remove rubber from airplane tires from an airport runway surface. The apparatus uses a rotary manifold to discharge water jets under high pressure (at least 20,000 psi, with a preferred range of 35,000 psi to 55,000 psi). A hydraulic motor is used to rapidly rotate the manifold so that the jets travel at high speed relative to the surface (e.g., ninety to one hundred miles per hour). As a result of this short dwell time, high water jet pressures can be used without damaging the surface. The device employs a shaft and seal assembly specially designed to operate at these high speeds and pressures. The device is limited to treating horizontal surfaces, and over a relatively narrow path width.
Treating a surface such as a ship hull is much more complex than treating a horizontal surface such as an airport runway. A ship hull is not planar, thus the device must be able to conform to convex and concave surfaces. Gravity can not be used to bias the apparatus against the ship hull, thus an artificial system must be created to keep the apparatus a fixed distance from the surface being treated. The apparatus must be capable of covering a large surface area in a short period of time. When cleaning a ship hull time is of the essence to reduce dry dock costs. When cleaning a storage tank it is important to reduce the man hours needed to clean the tank. The apparatus must be capable of treating the surface with high quality and high reliability, so that the treated surface passes inspection and need not be retreated. The apparatus must be economical to construct and operate, and must have a long operation life between repairs. Finally, the apparatus must be capable of being operated by persons of ordinary skill.